1. Field of the Invention
The present invention relates to a shadow mask deposition system and method for forming electronic elements on a substrate and, more particularly, to forming via holes in a shadow mask deposition process.
2. Description of Related Art
Generally, in a multi-layer electronic device, such as a semiconductor device, a via is needed to provide a conductive path through a non-conductive layer (insulator or dielectric layer), in order to connect two or more conducting layers. A via is a structure formed by filling or lining a via hole (or through-hole) with conductive material, which is used to electrically connect two or more conducting layers in a multi-layer substrate.
The creation of vias in typical microcircuit fabrication processes is accomplished by applying a pattern or stencil of etch resistant material over the layer through which the via is to be formed and subsequently applying an etching medium to the wafer to remove areas unprotected by the etch resistant material. The etch resistant material, known as photoresist, is patterned by a process called photolithography, which is a subtractive wet chemical process.
Because photolithography is a subtractive process, it is a process that lends well to the formation of via holes in the manufacture of multi-layer electrical devices. The multi-layer electrical device fabrication process includes numerous deposition and etching steps in order to define appropriate patterns of conductors, insulators and vias. Exemplary photolithography processing steps that produce vias in a multi-layer electrical device include: applying a photoresist pattern of via holes upon an insulator layer; developing the image whereupon photoresist remains everywhere except at the via locations; baking the image; etching the structure whereupon the etching material dissolves the insulator layer but not the photoresist, thereby forming a hole in the insulator layer in the areas where there is no photoresist without damaging an underlying conductor; and removing the remaining photoresist which leaves the insulation layer (with via holes therethrough) on top of the underlying conductor. As can be seen, the multi-layer electrical device fabrication process utilizes numerous deposition and etching steps in order to define one or more appropriate patterns, especially vias.
Because of the number of steps required to form multi-layer electronic devices, such as semiconductor devices, with the photolithographic manufacturing process, foundries of adequate capacity for volume production are very expensive. Furthermore, because of the nature of the fabrication process, the production equipment must be utilized in a class one or class ten clean room. In addition, because of the amount of equipment needed and the size of each piece of equipment, the clean room must have a relatively large area, which can be relatively expensive.
A vapor deposition shadow mask process is well known and has been used for years in microelectronics manufacturing. The vapor deposition shadow mask process is a significantly less costly and less complex manufacturing process compared to the photolithography process. However, in contrast to the photolithography manufacturing process, the vapor deposition shadow mask process is an additive process that is performed in a vacuum environment. In order to form a pattern by shadow mask vacuum deposition, an opening (aperture) is required in the mask to allow material to pass therethrough. However, to make a non-deposit area (such as a via hole), a blockage is needed in the mask to block the area from material being deposited thereon. Therefore, in order to make a via hole, a land mass in the form of an unconnected island is needed to block the via location. This is not possible with a shadow mask because there would be no material to support the blocked area.
Furthermore, a continuous inline, reel-to-reel shadow mask deposition process, which is an additive process, presents a technical challenge in making via holes without disrupting the process. For example, it is inefficient and impractical to insert one or more photolithography steps into a highly efficient inline, reel-to-reel shadow mask deposition process.
Therefore, what is needed, and not disclosed in the prior art, is a method and apparatus for forming a via hole in an automated shadow mask vacuum deposition process.